21 April 2017

Helium nanodroplets shed light on phase separations in other materials

Long-time decay of the NMR amplitude arising from solid helium-three that tracks the loss of the solid component to the formation of degenerate Fermi liquids in nanodroplets. Long-time decay of the NMR amplitude arising from solid helium-three that tracks the loss of the solid component to the formation of degenerate Fermi liquids in nanodroplets.

Observing growth processes in classical alloys is extremely difficult; scientists overcame this by studying quantum systems.

First, some background

Phase separations are fundamentally important in condensed matter physics because they play a major role in the preparation of new materials, including high-strength metal alloys. However, these transitions occur in a kind of "slow motion" — typically over days or years. This makes them hard to measure and limits what we know about phase separations in these materials.

What did scientists discover?

Scientists decided to look at phase separations in quantum fluids in order to shed light on a classical phase transition, thermal diffusion in metallic alloys.

Using high-sensitivity, ultra-low-temperature nuclear magnetic resonance (NMR) techniques, the scientists studied the phase separation of very dilute solutions of one kind of helium isotope (helium-3, or 3He) in another (helium-4, or 4He).

At densities as low as 16 parts (of 3He) per million (of 4He), the 3He atoms formed tiny "nanodroplets." The smallest droplets slowly shrunk as 3He atoms diffused through the solid 4He matrix, causing the small droplets to form larger droplets. In this so-called "coarsening" period (known as "Ostwald ripening"), the growth rate of the droplet size (and hence the decay rate of the NMR signal) is determined by the capture at the surface of the droplet, which leads to a one-third power law as a function of time.

Why is this important?

Scientists overcame their inability to study "slow-motion," classical thermal diffusion in metallic alloys by studying a surrogate system: quantum diffusion in 3He-4He, which occurs orders of magnitude faster.

THE TOOLS THEY USED

This research was conducted in the Bay 3 MicroKelvin Laboratory at the MagLab's High B/T Facility located at the University of Florida.

Who did the research?

D. Candela1, B. Cowan2, C. Huan3, L. Yin3, J. S. Xia3, N.S. Sullivan3

1University of Massachusetts (Amherst) ; 2Royal Holloway, University of London; 3University of Florida

Why did they need the MagLab?

Specialized, ultra-low-temperature NMR techniques, available only at the MagLab’s High B/T Facility, offer the high sensitivity scientists need to make these measurements. As shown in the figure above, the sample is placed at the end of a probe in crossed NMR coils, which are close to low-temperature electronics that amplify the weak signal.

Details for scientists

Funding

This research was funded by the following grants: G.S. Boebinger (NSF DMR-1157490); B. P. Cowan (EPSRC-Award EP/E023177/1); N.S. Sullivan (NSF DMR-1303599)


For more information, contact Neil Sullivan.

Details

  • Research Area: Condensed Matter Technique Development, Magnet Resonance Technique Development, Quantum Fluids and Solids
  • Research Initiatives: Materials
  • Facility / Program: High B/T
  • Year: 2017
Last modified on 21 April 2017